Results from a Survey of Gravitational Microlensing toward M31

We describe the results of a search for microlensing events affecting starsin the outer bulge and inner disk of M31, due both to masses in M31 and theGalaxy. These observations, from 1994 and 1995 on the Vatican AdvancedTechnology Telescope and KPNO 4m, are sufficient to rule out masses in therange of ~0.003 M_sol to 0.08 M_sol as the primary consistuents of the mass ofM31 towards this field. Furthermore we find six candidate events consistentwith microlensing due to masses of about 1 M_sol, but we suspect that some ofthese may be cases where long-period red supergiant variables may be mistakenfor microlensing events. Coverage from anticipated data should be helpful indetermining if these sources maintain a constant baseline, and therefore arebest described by microlensing events.Comment: Astrophysical Journal Letters, in press (accepted 8 Oct 1996), 14 pages, Latex, 4 required .sty files, 3 figs